void conj(char* s1, char* s2) {
    int sz2 = strlen(s2);
    int sz1 = strlen(s1);
    int count = 0;
    //向后推s1个字符，防止被数据覆盖
    for (int i = 0; i < sz1; i++) {
        s1[i + sz1] = s1[i];
    }
    //num1,num2分别表示s1,s2中已经排列好的字符数void
    int sz = sz1;
    int num2 = 0;
    int num1 = 0;
    //count 表示新字符串的下标
    while (num1 < sz1 && num < sz2) {
        if (!(count % 2) && count < 2 * N) {
            s1[count++] = s1[sz++];
            num1++;
        }
        else if(count % 2 && count < 2 * N){
            s1[count++] = s2[num2++];
        }
    }
    while (num1 <  sz1) {
        s1[count++] = s1[sz++];
        num1++;
    }
    while (num2 < sz2)
        s1[count++] = s2[num2++];
   
    s1[count] = '\0';
}